Electrolytic resistor



Nov. 11, 1941. D. N. CRAIG 2,261,974

ELECTROLYTIC RESISTOR Filed July 25, 1940 INVENTOR,

ATTORNEY cults.

Patented Nov. 11, 1941 David Norman Craig, Washington, D. 0., assignor to Government of the United States of America, as represented by the Secretary oi Commerce Application July 25, 1940, Serial No. 347,470

40mins. (Cl. 201-63) (Granted under the act of March 3, 1883, as

' amended April 30, 1928: 370 0. G. 'l5l') The invention described herein may be manu factured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon,

This invention relates to improvements in electrolytic resistors of the type disclosed in the copending application for United States Letters Patent of Francis W. Dunmore, Ser. No. 247,242, iiled'December 22, 1938 (Patent No. 2,210,903, granted August 13, 1940), and aims generally to improve the same.

Electrolytic resistors of many types and kinds have been made in the past, but most of them were subject to limitations of polarization, gassing, non-uniformity, or lack of permanence. The us of electrolytic resistors has been conlined, therefore, to applications in which these detrimental features were not objectionable or for which they possessed some positive advantags. Because of polarization and gassing when used with direct currents, electrolytic resistors are more generally associated with A.-C. cir- However, certain types may be used successiully in 11-0. circuits, and this invention aims to provide a type developed primarily for temperature indicators and particularly though not exclusively applicable to use on radio meteorographs where variable direct currents are used.

Electrolytic resistors for this purpose require (1) a large temperature coefficient, (2) a freezing point below any probable atmospheric temperature, (3) light weight, (4) reversibility of electrochemical reactions, (5) stability of calibration, (6) hermetical sealing, .(7) high resistance with a minimum of inductance and capacitance, and (8) rapid respons to temperature changes. The use of electrolytic resistors such as those describedherein is by no means limited to radio meteorographs. Because of their stability and high-temperature coefllcients they are adapted for the control of temperatures when the current tions proved to be somewhat unsatisfactory because of polarization and the evolution of gas, the latter requiring that the resistors be provided with expansion chambers or vents.

By the present invention, however, these dithculties are overcome and all eight of the above mentioned desiderata are provided for, severally and collectively.

In the accompanying drawing of a preferred embodiment of the invention, the single figure is an elevation view of a general embodiment illustrative oi the same.

In the form shown in the drawing. a capillary U-tube E0 of approximately 1 millimeter bore serves to hold the solution and the electrodes 5 6. Small bulbs i2 and I3 are blown or otherwise formed at either end of the U-tube It to receive the electrodes, and in this embodiment are provided with capillary necks M. This tube may be filled with the electrolyte to the upper ends of the bulbs 12, i3, in. any suitable manner, as by a small pipette drawn out to a. line capillary. Preferably a small bubble 15 of gaseous fluid is left in one or both of the bulbs l2, 53, which ac commodates expansion.

Th present invention contemplates that the resistance of the tube may be controlled by vary passing through the cell is very small. Experlments using alternating current and such a cell for controlling temperature in a water bath in conjunction with a radio amplifier and small thyratron show that regulation to about 0.005? C. can beobtained and this is probably susceptible of improvement. Because of their high reing the electrolyte, or by standardizing the electrolyte and varying the length of the capillary In. The electrodes, in this case pieces oi size 18 (American wire gauge) annealedcopper wire, are inserted through the capillary necks I4 and project into the electrolyte in the bulbs l2, l3, and are suitably sealed into the capillary necks ll. A De Khotinsky cement seal is satisfactory, when a sufllcient length (say 2 or 3 inches) of capillary neck It is provided.-

In accordance with this invention the complete resistor, when not in use, is short-circuited by connecting the. ends of the electrodes in any suitable manner as by a wire l6, for the purpose of removing any difl'erence in potential between the two electrodes and causing the composition of the solution surrounding the electrodes to gr. 1.18), ethyl alcohol and cuprous chloride. as shown in Tablel.

' ished resistors.

Tsar: 1.-Resistivities of solutions containing! concentrated hydrochloric acid, ethyl alcohol,

and cuprous chloride The hydrochloric acid and alcohol mixtures were prepared by volume; the sum of the volumes taken was '75 ml. to which 2 g. of cuprous chloride were added. The solutions subsequently were 'duction of the cupric ion to cuprous ion by the copper electrodes or allowance therefor. when reduction is completed the solutions become colorless.

The resistivities of the solutions were measured on a bridge using 60-cycle current and an A.-C. galvanometer as the detector. The ratio arms were equal and each consisted of a 100,000-ohm standard resistor. The other arms consisted of a variable resistor and the cell containing the solution to be measured. The accuracy of the measurements on this bridge was determined by comparisons with resistors 01 low inductance and capacitance which were standardized by others in a suitable manner. When making A.-C. measurements the error in measuring 100,000-hm resistors did not exceed 3 percent at 60 cycles. The error in measuring 100,000-ohm resistors with direct current did not exceed 0.03 percent. Most of the measurements on electrolytic resistors given in this description are D.C. measurements.

A specially designed cell was used for measuring the resistivity of the solutions. It consisted of a test tube which contained the solution to be measured, and a capillary tube, supported at the top, dipped into this solution. The electrodes were copper, one being in an enlarged portion of the capillary and the other in the free liquid near the lower end of the capillary. This arrangement was convenient for making exploratory measurements at extremely low temperatures and permitted measurements to-be made under conditions similar to those obtaining in the fin- The constant of this cell was determined with suilicient accuracy by comparative measurements with a conductivity cell oi the customary type for which the constant was known.

The resistance measurements employing direct current were made on the same bridge as the resistivity measurements.

For the D.C. measurements the bridge was provided with a sensitive D.C. galvanometer and a source oi variable voltage and in some cases a low-resistance mlcroammeter was in eries with the resistor so that the current and voltage could be correlated. I

Measurements above 0 C. were made with the resistors immersed in a beaker of water which was surrounded by a larger beaker and the intervening space filled with loose cotton. The stirring was done manually and the temperature was maintained suiliciently constant for the purpose by the addition of small quantities of hot or cold water. The temperature was measured with a mercury thermometer graduated to 0.l C. The measurements at 0 C. were made with the resistors immersed in mixtures of ice and water. Measurements below 0 C. were made with the resistors immersed in ethyl alcohol contained in a clear-glass Dewar to which solid CO: was added as required. Six or more observations of temperature and resistance were made while the temperature of the alcohol was held close to the average value by the addition of small quantities of CO: and frequent stirring. The temperatures below 0C. were estimated to 0.1" C. with a toluene thermometer graduated to 1 C.

The compositions oi the solutions investigated and their resistivities at 300 and 0 C. are given in Table 1. The resistivity values at 30 C. were measured with Gil-cycle current, employing the resistivity cell previously described. The resistivities at 0 were calculated by multiplying the resistivity values at 30 C, by the ratio of the A.-C. resistances at 0 and 30 of resistors containing the respective solutions.

The resistivity of the solutions varies comparatively little with changes in the copper content. For this reason the data given in Table i can serve as a guide in making resistors of specifled value notwithstanding the fact that a small amount of cupric ion was known to be present when the measurements were made. 1

Many tests were made of devices according to this invention, establishing that by the particular combination above set forth the several desiderata above mentioned are attained. The details 0! such tests, while not necessary to the present disclosure, have been published within two years prior to the present application in Research Paper R. P. 1126, part of the Journal of Research 0!. the National Bureau of Standards, vol. 21 (Aug. 1938), p ges 225 et seq., to which reierence may be had for test and other data to supplement the present description.

In this connection it is believed sumcient here to summarize the results of such tests, which. as shown in Research Paper R. P. 1128, established that the present invention provides a unique combination of copper electrodes in an electrolyte consisting oi a solution of copper chloride and hydrochloric acid in water and alcohol, in which the acid is present in an amount eflectively reventing the lyte'irom becoming basic at the anode electrode during use, in which the copper chloride is present in an amount sup plying adequate quantities of ions at +30 0., and inwhich the alcohol is present in an amount sufllcient to maintain the freezing point of the electrolyte below -75 C., and in such additional. amount as to adjust the resistance of the electrolyte to a value such t at the column of electrolyte in the thin-walle capillary tube which is rapidly responsive to temperature changes may be longenough to control the resistance of the resistor substantially to the exclusion of the resistance of the solution in the enlarged end chambers, said value being such that the thin-walled capillary tiibe need not be so long as to be unduly fragile. This device, as indicated in more detail in said research paper, is reliably responsive to temperature over a range from +30 C., to 75 C., without gassing and without'formation of precipitates which might clog the capillary tube.

While, for illustrative purposes, I have disclosed one satisfactory methodof sealing tubes for certain purposes, the invention in its broader aspects is not limited to any particular form of seal. For example, where permanency is important, a copper to glass seal can be made, in

which case one terminal can be copper wire, and I the other terminal a small copper tube to permit filling the cell after the copper'to glass seals have been made, by evacuating. the unit, filling it through the copper tube, and then closing the upper extremity of the tubing.

I claiin as my invention:

1. In an electrolytic resistor of the type employing a capillary column of electrolyte connecting a pair of spaced electrodes, the combination of copper electrodes and an electrolyte consisting essentially of an aqueous solution containing substantial proportions of hydrochloric acid, ethyl alcohol and cuprous chloride.

2. In an electrolytic resistor of the type employing a capillary column of electrolyte connecting a pair of spaced electrodes, the combination of copper electrodes and an electrolyt consisting essentially of a. mixture of approximately 1 part 36% aqueous solution of hydro- ,chlorlc acid, to 4 parts ethyl alcohol and about 2 /2 grams per 100 mL'of cuprous chloride.

3. As an article of manufacture, an electrolytic resistor of the type employing a. capillary column of electrolyte connecting a pair of spaced electrodes, comprising the combination of copper electrodes, an electrolyte containing copper ions and an electrically conductive connection from one electrode to the other for short circuiting the same and causing the composition of those parts of the electrolyte surrounding the two electrodes to become uniform.

4. An improved electrolytic resistor particularly adapted for temperature indicators of radiometeorograph instruments consisting of a thinwalled capillary glass tube of approximately one millimeter bore communicating with enlarged chambers at its ends; a copper electrode in each of said chambers; an electrolyte filling said capillary tube and substantially filling said chambers, said electrolyte consisting of a solution of copper chloride and hydrochloric acid in water and alcohol in which the acid is present in an amount effectively preventing the electrolyte from becoming basic at the anode. electrode during use, in which the copperchloride is present in an amount supplying adequate quantities of ions at +30 C., and in which the alcohol is present in an amount sufiicient to maintain the freezing point of the electrolyte below C., and in such additional amount as tov adjust the resistance of the electrolyte to a value such that the column of electrolyte in thethin-walled cap-- illary tube which is rapidly responsive to temperature changes may be long enough to control the resistance of the resistor substantially to the exclusion of the resistance of the solution in the enlarged end chambers, said value being such that the thin-walled capillary tube need not be so long as to be unduly fragile; said resistor being reliably responsive to temperature over a range from +30 C. .to 75 C., without gassing and without formation of precipitates which might clog the capillary tube.

. DAVID NORMAN CRAIG. 

